To some extent, it depends on what control scheme Zelda U goes with. Assuming we're playing predominantly or only with the GamePad, I'm a fan of having just one or two slots to use with buttons, swapping out items with the touch screen. So long as you've got it all at your fingertips, why not make use of it? Otherwise, a radial menu like Skyward Sword's shouldn't be hard to pull off again. Left control stick moves Link, right control stick briefly stops doing whatever it normally does and selects the item on the circle. Bam, done. If we're forced to use only buttons, my vote is "as many slots as we can without over-complicating the controls."
I'm pretty confident Nintendo will think of something convenient, so I'm not too worried about it.